Eel Grass (aka wild celery, tape grass)

Eel grass is a very common Connecticut River submerged aquatic;
it grows in 4-6 ft of water. Long grass-
like leaves (ca. 3 ft in length) grow from creeping stems rooted
in the river bottom. Submerged eel grass
meadows are inhabited by a variety of fish, including, of course,
large, fat American eels.

Sexual reproduction in eel grass is complex and interesting, even
for a plant!

Populations of eel grass consist of two genders: males and
females. These genders are identical with
regard to vegetative characteristics; they differ only in the
nature of the flowers they form. The male plants
form very small flowers (0.6 mm across, there are 25.4 mm to the
inch!) in which only the stamens are
functional (staminate flowers). The staminate or male flowers
are found on a small inflorescence that
develops from the submerged stem. A staminate inflorescence may
form 2,000 staminate flowers. When
the staminate flowers are mature, they are cut off (abscission)
from the inflorescence and float to the river’s
surface. The staminate flowers are now free-floating and are
carried about the river’s surface by the
vagaries of wind and current; essentially they are small boats of
pollen whose task is to bump into a female
flower.

While the male plants are releasing thousands of
free-floating staminate flowers, the female plants
have formed long flower stalks that reach the water’s surface.
At the ends of these stalks single flowers are
formed in which only pistils are functional (pistillate flowers).
Pistillate flowers remain attached to the
female plant via the long flower stalk. The flowers float on the
surface, more or less at a slant, causing
slight depressions in the surface of the water, a kind of dimple
in the surface. Staminate flowers that
happen to be floating nearby slide into this small depression or
dimple in the water’s surface and make
contact with the pistillate flower. Pollen is transferred to the
female pistillate flower (pollination). The
pollen grains germinate and ultimately sperm nuclei and eggs
unite and fertilization occurs. The pistillate
flower’s ovary increases in size to become a small fruit within
which are 200-400 seeds, each with a young
embryo (the product of fertilization).

The female plant, sensing in some way that pollination and
fertilization have occurred (not magic,
only biochemistry), starts to pull the fruit underwater! The
flower stalk starts to coil like a bed spring, the
fruit to which it is attached is slowly pulled beneath the
River’s surface into the safety of its depths.

The following diagram gives an overview of sex in
VallisneriaDiagram:Sex in eel grass

After reading (and I hope following) all this, you must be
wondering why eel grass has evolved
such a chancy and complex sexual cycle; it could have just as
easily evolved flowers that self-pollinated,
i.e. had functional stamens and pistils. In fact, why does eel
grass bother with sex at all? It can easily
reproduce vegetatively by growing more stems.

This can all be formulated into an interesting biological
question, “How is cross-pollination
advantaged over vegetative propagation in eel grass?”

Answer this question and (this is the hard part)
scientifically prove your answer and you are on
your way to fame and glory!

One last fact: Eel grass is not a true grass (family
Gramineae) but is in the family
Hydrocharitaceae.

Bibliography

Kausik, S. B. (1939) Pollination and its influences on the
behavior of the pistillate flower in
Vallisneria spiralis. American Journal of Botany
26:207-211.